1. Field of the Invention
The present invention relates to an apex seal for rotary piston engines. More particularly, the present invention, pertains to an apex seal made of an iron-based material.
2. Description of Prior Art
In rotary piston engines, working chambers are separated from each other by means of side seals provided on side surfaces of rotors and apex seals provided on apex portions of the rotors. Among these seals, the apex seals are slidably moved at very high speeds along the inner wall surfaces of the rotor housings and besides they are also subjected to influences of combustion gas pressure, inertia force and spring force which tend to force strongly the apex seals against the inner wall surfaces of the rotor housings. Thus, the apex seals are required to have superior wear-resistant property.
Conventional rotary piston engines use apex seals which are prepared in accordance with the process as taught by Japanese patent publication No. 48-25290 published on July 27, 1973. According to the teachings by the Japanese patent publication, a cast iron blank is subjected to an electron beam embodiment to have a part of the blank material molten and thereafter the blank is quenched so that the molten material is solidified. In the course of solidification, a chilled structure is formed due to the chilling effect of the part of the blank where the material is not molten. It has been proved that the apex seal formed under this process has a good wear-resistant property. It should however be noted that the hardness and therefore the wear-resistant property of this material decreases under a high temperature. In view of the fact that recent high power rotary piston engines are operated under a high speed and high output power so that the conventional apex seals show insufficient wear resistant property for such high power rotary piston engines.
Japanese patent publication No. 49-30895 discloses on alloy having a high wear-resistant property. This alloy has a hard matrix metal containing hard inter-metal compounds dispersed in the matrix metal for providing an improved wear-resistant property. However, this type of material is not suitable for apex seals of rotary piston engines because the material has a poor thermal shock resistance so that apex seals made of this material are apt to produce cracks when they are subjected to repeated heating and cooling.